docs: def set_ax_spines(ax=None, *, c="k", lw=3, zorder=10):
      """Easily set the properties of all four axis spines.
  
      Parameters
      ----------
      ax : matplotlib AxesSubplot object (optional)
          Axis to set. If None, uses current axis. Default is None.
      c : any matplotlib color argument (optional)
          Spine color. Default is k.
      lw : number (optional)
          Spine linewidth. Default is 3.
      zorder : number (optional)
          Spine zorder. Default is 10.
      """
      # get ax
      if ax is None:
          ax = plt.gca()
      # apply
      for key in ["bottom", "top", "right", "left"]:
          ax.spines[key].set_color(c)
          ax.spines[key].set_linewidth(lw)
          ax.spines[key].zorder = zorder